Cooking apparatus



Oct. 17, 1950 F, GROSS 2,526,226

COOKING APPARATUS Filed Jan. 11, 1947 Mun/7'01? FRITZ 4. $3055 Patented Oct. 17, 1950 COOKING APPARATUS Fritz A. Gross, Weston, Mass., assignor to Raytheon Manufacturing Company, Newton, Mass., a corporation of Delaware Application January 11, 1947, Serial No. 721,591

6 Claims.

This invention relates to cooking apparatus, and more particularly to a means for illuminating the interior of a microwave oven.

It is often desirable to illuminate the interior of an oven in which food is being cooked, while the food is being cooked, in order to follow the cooking operation. This illumination must be done by artificial means in the case of a microwave oven which is a completely enclosed metallic cavity.

In providing such artificial illumination, it is desirable to prevent radio-frequency energy from striking the lamp which is used as the light source,

adverse effect on the lamp envelope and the electrode structure within said envelope. At the same time, it is desirable, for purposes of efficiency, to not allow any of the microwave energy to escape from the interior of the enclosure, so that substantially all of said energy goes into heating of the food.

It is, therefore, an object of the present invention to devise a means for artificially illuminating the interior of a microwave oven.

Another object is to devise a means for illuminating, by means of a lamp, the interior of a radio-frequency cavity, such means effecively preventing radio-frequency energy from striking said lamp.

A further object is to devise an illuminating arrangement for the interior of a radio-frequency cavity, said arrangement being adapted to prevent any appreciable loss of energy within the cavity, or escape of energy from within the cavity.

The foregoing and other objects of the invention will be best understood from the following description of an exemplification thereof, reference being had to the accompanying drawing, wherein the single figure is a vertical section throvgh a device according to the invention.

A hollow rec angular prismoidal enclosure or cavity I is made of a suitable metal and has rather thin walls asshown'; enclosure I is adapted to serve as the oven of the cooking apparatus. Oven I is adapted to have a container 2 of food placed therein, said container resting on the bottom wall of the oven while the food is being cooked. In order to allow access to the interior of the oven for placing the food therein and for removin the food therefrom, a rectangular opening 3 is provided in the front wall of the oven I, this opening being closable by means of a hinged metal door 4. When door 4 i closed, the enclosure I is entirely closed, except for the opening I2 for the exciting means to be described hereinafter.

Numeral 5 generally designates an electron-discharge device of the magnetron type, which includes, for example, an evacuated envelope 6 made of highly conductive material, such as copper, and provided with a plurality of inwardly-directed. radially-disposed anode vanes I. The arbecause such energyordinarily has a damaging or rangement is such that each pair of adjacent anode vanes forms, together with that portion of the envelope lying therebetween, a cavity resonator, whose natural resonant frequency is, as is well known to those skilled in the art, a func ion of the geometry of the physical elements making up the same. For the purposes of the present invention it is desirable that the dimensions of each such cavity resonator be such that the wavelength of the electrical oscillations adapted to be generated therein has a predetermined value, for example, oi' the order of ten centimeters. Wave: lengths of this order lie in the microwave region of the frequency spectrum. However, this invention is equally applicable to radio-frequency energy of longer or shorter wavelengths within or without the microwave region.

Centrally located in envelope 6 is a highly electron-emissive cathode member 8, for example, of

the well-known alkaline-earth metal-oxide type, said cathode member being provided with conventional means (not shown) for raising the temperature thereof to a level sufficient for thermionic emission.

The electron-discharge device 5 is completed by magnetic means (not shown) for establishing a magnetic field in a direction transversely of the electron path between the cathode and anode members thereof.

Magnetron 5 is energized from any suitable source (not shown) and when so energized delivers microwave energy having a predetermined wavelength to a coaxial transmission line 9, the inner conductor III of which is coupled to oscillator 5 by a loop II and the outer conductor of which is connected to envelope 6. The inner inductor I0 of line 9 extends directly into the interior of oven I through a suitable opening I2 provided in the rear wall thereof, while the outer conductor of said line is connected to the rear wall of the ov"n I by a suitable fastening means I3. Opening I2 is preferably centered with respect to he vertical sidewalls of the oven, and is preferably somewhat above the horizontal mid -plane of the oven.

An aperture I4 is provided in the top wall of oven I, said aperture being circular, fo xample, and having a diameter d. Aperture I4 is closed by a disk I5 of a material which is transparent to lightand which has a low radio-frequency loss factor, such as a certain commercially-produced glass having a very low thermal coefiicient of expansion, for example. Extending upwardly or outwardly from the to wall Of oven I is a hollow metallic tube I6 which has an internal diameter equal to d.

oven I, thereby artificially illuminating the interior of said oven.

High-frequency electromagnetic or microwave energy is fed by coaxial line 9 and exciting probe or rod Ill, from magneron osc llator to the interior of oven or cavity I. The diameter d of a erture Hi and of tube I6 is made such that, for the wave mode present in cavity I, the cut-off wavelength of tube :6, considered as a hollowwaveguide, is below the wavelength of the oscillations generated by o cillator 5. The cut-01f wavelength for hollow waveguides depends on the cro s-sectional dimen ions of such guides, as is well-known to those skilled in the art.

S nce the cut-off wavelen th of tube 16 is designed to be b low the wavelength of the radiofrequency oscillations of source 5, such oscillations will not propagate down tube l6 as a hollow waveguide. Therefore, microwave energy will not be transmitted away from the interior of the enclosure to be lost for cooking purposes to thereby produce a loss of efficiency. Also, since radio-frequency energy is not transmitted down tube Hi. there will be no chance for such energy to impinge on lamp I! to thereby damage the same.

As stated above, disk I5 is made of a material which has a low radio-frequency loss factor. Therefore, only a very insignificant portion of the total microwave energy in cavity I will be wasted in heating said disk, and the disk will not reach a very high temperature wh le the radio-frequency energy is being supplied to the oven.

It is within the scope of this invention to make the aperture IA of any desired shape, the disk l5 having a corresponding shape and element l6 having an opening therethrough of a corresponding configuration. For example, aperture [4 may be rectangular and element I5 may have a hollow rectangular cro s-section, in which case the cut-off wavelength formulae for rectangular hollow waveguides would be used to calculate the internal dimensions of portion l6 so as to make the cut-off wavelength of waveguide portion l6 less than the wavelength of the oscillations of oscillator 5.

It will be seen, from the above description, that I have provided a structure for artificially illuminating the interior of a microwave oven, by the use of which the light source is protected from radio-frequency energy, and the absorption of radio-frequency energy from the food is kept down to a minimum.

Of course, it is to be understood that this invention is not limited to the particular details as described above, as many equivalents will suggest themselves to those skilled in the art. It is accordingly desired that the appended claims be given a broad interpretation commensurate with the scope of this invention within the art.

What is claimed is:

1. Cookin apparatus, comprising: an oven consisting of a metallic enclosure, means for supplying high-frequency electromagnetic waves to the interior of said oven, said oven having an aperture in one wall thereof, a hollow metallic waveguide aligned with said aperture and extending outwardly from said oven, and a source of light external to said oven in such a position as to project light through said waveguide and 7 said aperture into said oven.

2. Cooking apparatus, comprising: an oven consisting of a metallic enclosure, means for supplying high-frequency electromagnetic waves of a predetermined wavelength to the interior of said oven, said oven having an aperture in one wall thereof, a hollow metallic waveguide aligned with said aperture and extending outwardly from said oven, and a source of light external to said oven in such a position as to project light through said waveguide and said aperture into said oven, said waveguide having such interior dimensions that the cut-off wavelength thereof is less than said predetermined wavelength.

3. Cooking apparatus, comprising: an oven consisting of a metallic enclosure, means for supplying radio-frequency electromagnetic waves to the interior of said oven, said oven having an aperture in one wall thereof, a transparent closure of a low radio-frequency loss material positioned in said aperture, and a source of light external to said oven in such a position as to project light through said closure into said oven.

4. Cooking apparatus, comprising: an oven consistin of a metallic enclosure, means for supplying radio-frequency electromagnetic waves to the interior of said oven, said oven having an aperture in one wall thereof, a transparent closure of a low radio-frequency loss material positioned in said aperture, a hollow metallic waveguide aligned with said aperture and extending outwardly from said oven, and a source of light external to said oven in such a position as to project light through said waveguide and said closure into said oven.

5. Cooking apparatus, comprising: an oven consisting of a metallic enclosure, means for supplying radio-frequency electromagnetic waves of a predetermined wavelength to the interior of said oven, said oven havin an aperture in one wall thereof, a transparent closure of a low radiofrequency loss material positioned in said aperture, a hollow metallic waveguide aligned with said aperture and extending outwardly from said oven, and a source of light external to said oven in such a position as to project light through said waveguide and said closure into said oven, said waveguide having such interior dimensions that the cut-off wavelength thereof is less than said predetermined wavelength.

6. Cooking apparatus, comprising: an oven consisting of a metallic enclosure, means for Sunplying high-frequency electromagnetic waves of a predetermined wavelength tothe interior of said oven, said oven having an aperture in one wall thereof, and a source of light external to said oven in such a position as to project light through said aperture into said oven, the dimensions of said aperture being such that the cutoff wavelength thereof is less than said predetermined wavelength.

FRI'I'Z A. GROSS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,364,526 Hansell Dec. 5, 1944 2,370,161 Hansen Feb. 27, 1945 2,408,295 Cossin, Sept. 24, 1946 

